Filament emission electrode and method of minimizing filament stresses therein



Filed June 20, 1951 MINIMIZING FILAMENT STRESSES THEREIN Sept. 2 2, T953 Patented Sept. 22, 1953 FILAMENT EMISSION ELECTRODE AND METHOD OF MINIMIZING FILAMEN'I STRESSES THEREIN Lloyd R. McIntosh, Winchester, Mass., assignor to High Voltage Engineering Corporation, Cambridge, Mass., a corporation of Massachusetts Application June 20, 1951, Serial No. 232,602

21 Claims. (Cl. 313-245) This invention relates to emission electrodes of the hairpin type of filament, and also to the minimizing of stresses therein, particularly those due to expansion and contraction in use, and to means for preventing jarring of the filament in use.

In order that the principle of the invention may be readily understood, I have illustrated in the accompanying drawing a single embodiment of the said emission electrode assembly and the filament thereof, and I have somewhat diagrammatically indicated the series of steps involved in so constructing the said emission electrode and particularly the filament thereof, as to minimize filament stresses in the use of the said emission electrode and particularly those due to expansion and contraction in the filament in use.

In the drawing:

Fig. 1 is a vertical section upon the irregular line |l of Fig. 2 of the filament assembly, fastened together and representing the final step in the making of the filament; v

Fig. 2 is a top plan view of the filament assembly shown in Fig. 1;

Fig. 3 is a sectional detail through a portion of the upper part of the filament assembly, upon the line 3-3 of Fig. 2; and

Fig. 4 diagrammatically indicates the essential steps (excepting the final step indicated in Fig. 1) involved in so constructing or fashioning the filament of the emission electrode as to minimize filament stresses when in use, and particularly those due to expansion and contraction incident to the normal use and life of the filament.

While my invention is not limited to the particular. type of emission electrode herein illustrated and described, the invention is particularly adapted thereto, and therefore I will describe in detail the construction and the manner of making or manipulating such emission electrode including the filament without in all respects limiting myself thereto.

The filament of the emission electrode is indicated at I, and it is here shown as of hairpin type. It is preferably formed of tungsten and is desirably of a thickness on the order of .010 of an inch. In the use of the filament, stresses arise that cause breakage. There are or may be several causes of filament breakage. While all the stresses and the origin thereof that lead to filament breakage are not fully understood, my investigations, experiments and tests show that the principal stresses resulting in 2 breakage are caused by the expansion and contraction of the two arms of the filament l on both sides of the apex la thereof, rather than by the expansion of the apex itself. In other words, the breakage does not necessarily occur at the apex Ia.

My invention is not limited to a construction wherein a part of the filament is removed at the apex la. When part of the apex is removed, the thickness of the filament is reduced by one half at such area. This reduction in thickness apparently does not much increase the temperature at the apex, in the use of the emission electrode, and I have found that the danger of breakage is thereby increased. However, my invention is applicable whether or not a portion of the filament has been removed at the apex.

In actual operation, in use, the entire filament is heated to substantially the same temperature. Removal of a part of the apex may increase the temperature at that point or area, but, I find, only slightly.

I have discovered that breakage may occur at any point along the filament. The removal of part of the apex, I have found, increases the danger of breakage at that point, not because of increasing the heat at the apex, but because of reducing the mechanical strength of the apex.

In many applications of X-ray and cathoderay tubes, it is desirable to have a point source of electrons at the cathode. A simple manner of approximating a point source is to bend the filament which constitutes the cathode into a hairpin shape, so that most of the electrons emitted have their origin at the apex of the bend. When an electric current fiows through the filament, nearly all electrons emitted by the filament originate from or at the very small area of the said apex.

Whether or not a part of the apex is removed, there is always a tendency of the hairpin type of cathode to break, but not necessarily at the apex.

I have discovered that the tendency to breakage is very substantially reduced by forming a loop in the filament, preferably in each arm of the filament and desirably very close to the apex. I have obtained the best results by so forming each loop (if two loops are provided) that the inside diameter thereof is between 40 and thousandths of an inch, 40 thousandths being preferable. Desirably each loop (if two are provided) is located at a distance of, at most, one eighth of an inch from the apex.

It will be understood that the filament, in use, must and does undergo extreme changes of temperature. It expands and contracts every time it is heated up to emission temperature and is subsequently cooled. Consequently, the filament is subjected to stresses which may cause it to break. As I have stated, these breaks may occur at any point along the filament, and whatever the cause of the stresses in the filament, the forming of the loops minimizes this danger. I have found that the spring action of the two loops shown at 2, provided by me to minimize the damage of breakage, is such as to offer very little resistance to such expansion, and this fact I have ascertained as the result of my investigations, experiments and tests. Similarly as the filament i cools, the apex la and, I believe, the structure of the arms of the filament, contract, and again the spring action of the loop 2 minimizes the stresses in the apex la and elsewhere in the filament l.

It will be understood that the invention is not, however, limited to the particular type of emission electrode, but includes the provision and use of loops in any hairpin type filament, in order to minimize the danger of breakage either at the apex thereof or in either or both of the arms thereof.

I have, in the development and practice of my invention, at times formed only one loop, that is, in only one arm of the filament, but that is less satisfactory than forming one loop in each arm thereof, and as herebefore stated, quite close to the apex. As stated, apparently the principal stresses are caused by the expansion and contraction of the two arms of the filament, rather than by the expansion, or expansion followed by contraction, of the apex itself.

Furthermore, and as another feature of my invention, I have provided means to prevent jarring of the filament and at the same time elimihating the danger of molten glass on the filament arising when glass is used in the parts or connections between the lead in wires and the filament itself.

For an explanation of this feature of my invention, reference is made to Fig. 1. Therein the two arms of the filament i are indicated at 3, 3. To them, near their free ends, are secured, preferably by spot welding, two straight cold rolled steel rods 4, 4. It will be noted that the two arms 3, 3 of the filament l are secured to opposite sides of the respective rods 4, 4 so that the apex la is centrally located. This arrangement results from the peculiar shape of the completed filament as shown in the illustration of the two concluding steps involved in forming the hairpin filament as illustrated in Figs. 1 and 4, considered together, and yet to be explained. Small disks 5 of suitable shape, as for example circular, and which are preferably constructed of tantalum, are secured preferably solely by means of friction, to the two rods 4, 4, to prevent sputering of tungsten from the filament l onto the porcelain cylinder presently to be described. Between each shield 5 and such cylinder are spot welded onto the rods 4, 4, tungsten wires 6, 6, having a thickness on the order of .010 of an inch and bent into L shape as shown, and having the free end honed to a very sharp point. These points are spaced .010 to .20 of an inch from an aluminum disk l of suitable shape and size, secured in a face-to-face relation to the lower side of a porcelain cylinder 8 which I use instead of a glass elem nt. As shown in Fig. 2, the two steel rods 4, 4, extend directly through opening n 3 6 said cylinder 8 and they are rigidly secured thereto, as by means of cement. The said points of the wires 6, 6, which are directed toward the disk I serve as spark gaps to prevent the filament i from sudden surge discharges.

In use, I may provide a metal cup 9 to enclose or surround the filament l, excepting for the apex la thereof, during operation and it is desirably fastened by means of three screws I i to the said aluminum disk I and the said cylinder 8.

At their upper ends the steel rods 4, 4, are spot welded to lead-in nickel wires i2, i2, which are connected to a source of electric power (not shown) and which provides current for heating the filament I.

The said porcelain cylinder 8 assists in minimizing filament stresses, because it prevents jarring of the filament I, and, being of porcelain, it eliminates the danger of molten glass on the filament l. The cylinder 8 is solid except for the (herein) seven holes drilled therethrough for the two rods 4, the three screws I and the two projections i3 on the aluminum disk I. The holes i i in the cylinder 8 are shaped so as to fit snugly around the rods 4 which are cemented therein. The holes i4, may, for example be .070 of an inch in diameter at the narrow portion and .209 inch in diameter at the wide portion. The wide portion may be .135 inch deep and the height of the cylinder 8 is approximately one fourth of an inch. The holes for the screws ii, and one of which is indicated at it, are one eighth of an inch in diameter. The sockets l6, each of which receives a pin l3 of the aluminum disk '8 are of an inch in diameter, and one eighth of an inch deep, but they may be drilled entirely through the cylinder 8 if desired for convenience of manufacture. The cylinder 8 is desirably about 1-2 of an inch in diameter. The center of each hole M for reception of the rods 4, 4, is desirably located A; of an inch from the axial center of the cylinder 8. The center of each hole is for the screws H and of each socket Hi for the pins I3 is located .625 of an inch from the axial center of the cylinder 8.

While I prefer to construct the cylinder 0 of porcelain, I may construct it of Mykroy, with the rods 4, 4 cast in place. However Mykroy contains in addition to glass and mica a slight amount of plastic resin, which gives off enough Vapor to impair the vacuum within the cathode assembly. Still another construction which I may provide, is a cylinder such as 8, formed of steel, with the rods 4, 4 formed of Kovar sealed therein by means of glass-to-metal seals.

However, the use of glass seals is unsatisfactory because glass is fragile, and fragments thereof dislodged by a surge discharge, may drop onto the filament i, where the glass melts, adheres to the filament l, and increases the stresses in the said filament. Further, in such alternative embodiment, the rods 4, 4, are not secured with sufiicient rigidity to the cylinder 8, to prevent slight movement of the rods 4, 4, so that any jarring of the lead-in wires l2, I2, is transmitted through the rods 4, 4, to the filament i, and may cause the filament l to break.

The use of steel rods 4, 4, cemented to a porcelain cylinder such as 8 is preferable since it avoids all the herein above-mentioned disadvantages of Mykroy cylinders and Kovar-to- Iglass seals.

Referring to Fig. 1, the aluminum disk i has the same diameter as the cylinder 5 and is at most t; Of an inch thick. The holes I! therein correspond to the holes I in the cylinder 8 and are of the same diameter. The projections 13 fit loosely within the sockets I6, the diameter of the said projections I3 being slightly less than that of the sockets It so as to allow a little play, but preventing the disk I from coming into contact with the rods 4, 4. The holes I8, l8 in the aluminum disk 1 correspond to the holes M in the cylinder 8 but their diameter is slightly greater than that of the rods 4, 4, which pass therethrough.

The dimensions given are illustrative only and my invention is in no wise limited thereto.

It will be understood that the cylinder 8, the disk I and the metal cup 9 are fastened together by the three screws I I, only one of which is shown in Fig. 1. Each screw passes through a washer I9 at the top of the cylinder 8, and at its lower end it screws into a socket in the metal cup 9.

A small hole 2| in the center of the bottom portion of the metal cup 9 receives the apex Id of the filament I. The rods 4, 4 are one inch in height, the wide portion thereof being .125 of an inch in height and the extreme uppernarrow portion being of an inch in height.

Again I state that these dimensions are illustrative merely and my invention is not limited to such dimensions of parts. Moreover, if the cylinder is made of Mykroy instead of porcelain there is a slightly different construction and proportion of parts mainly with respect to the manner in which the rods 4, 4, are passed through the cylinder.

In Fig. 4, are diagrammatically illustrated the series of steps involved in the preferred manner of forming the two loops 2, 2 therein, excepting the final step indicated in Fig. 1. In Fig. 4 I have applied, as in Fig. 1, the numeral I to represent the entire filament, the numeral la to represent the apex when formed, and the numerals 2, 2 to represent the two loops. I have in Fig. 4 indicated five steps, a to e, in the carrying out of my invention herein disclosed and claimed, a final step of bending the ends of the two arms of the filament, being shown in Fig. 1.

The filament is formed, as shown at I, in step a of a short, straight piece of wire I, preferably of tungsten, and desirably a wire of .010 of an inch in thickness is employed. The tungsten wire may have a length of about two inches. Such wire I is then bent over a knife edge into the shape of a hairpin as represented in step I), wherein the apex is indicated at la. The two arms of the hairpin may then be squeezed together slightly near the apex, with a pair of pliers. If this is done, it would immediately follow step b.

In order to form the loops 2, 2 a special pair of pliers is employed, in which the clamping jaws consist of a pair of short rods of about .040 of an inch in diameter, and which are indicated by small circles at 22, 23 in step c. In carrying out said step 0, one arm of the hairpin is gripped between the two rods 22, 23 near the bend or apex la, and the said arm is bent by hand away from the other arm and around one of the said rods until the tungsten wire assumes the shape shown in step 0. Since the other rod of the pliers now prevents completion of the said first loop 2, the wire is then gripped as indicated in step d and the said first loop 2 may then be completed as shown in step d.

A similar loop 2 is then formed in the other .arm of the hairpin filament in such a manner that the second loop 2 is the mirror-image of the first loop .2 this step 01' the invention bein indicated at c. This arrangement simplifies mounting the completed filament in the cathode assembly shown in Fig. 1 and the centering of the apex of the filament therein, as has already been referred to.

Owing to the loops 2, 2, parts of the tungsten wire I may come in contact with other parts thereof. In order to prevent this, I may insert a knife blade in the crevices which I have marked 24 and 25 in step e, that is, where each. of the loop-s 2, 2 begins and terminates, and then twist them slightly so as to separate the said portions of the tungsten wire from each other, and thus leave the loops 2, 2 wholly free to expand and contract in the use of the herein claimed emission electrode.

Finally, the two arms 3, 3 of the filament are bent outwardly as indicated at 25, 21 in Fig. I, so that the finished filament has the form shown in Fig. 1 and it is ready to be made a part of the cathode assembly as shown in Fig. 1.

It will be evident from the foregoing description that this invention includes a filamentary electronic emitter of tungsten wire, of a diameter on the order of .010 of an inch and lying wholly in substantially the same fiat plane of the filaments diameter, said tungsten wire being bent at mid-length into hairpin shape having a small, sharp apex, the two arms of the tungsten wire each having a single loop only, each close to the said sharp apex, each of said arms extending straight both in front of and in the rear of the loop in said arm, each of said arms near its rear end being bent slightly outwardly, said bends being in opposite directions and providing short terminal portions that are for use of the filament welded to the opposite sides of two small-diameter straight rods respectively, the wall of each of said two loops being very slightly laterally twisted, only sufiiciently to be free from side contact with the adjacent straight portion of the arms respectively of the filament having such loop, to permit free expansion and contraction of said loops, said two loops being mirror images of each other and each lying in the plane of the rest of the wire emitter, the single plane in which the entire said tungsten emitter lies having a thickness exceeding the diameter of the tungsten wire only by the amount at the loops of the said slight lateral twisting of the walls of said two loops respectively, and at the ends. of the tungsten wire, by the diameter of the two small-diameter straight rods to which the ends of the tungsten wire are for use welded respectively, the entire filamentary emitter being of V-shape with slightly laterally bend ends that are for use welded to the opposite sides respectively of the smalldiameter straight rods.

Having thus disclosed the preferred embodiment and certain alternative constructions of the filament emission electrode of my invention, and the manner of constructing the same to minimize stresses in the filament, I desire it to be understood that although specific terms are employed, they are used in a generic and descriptive sense and not for purposes of limitation, the scope of the invention being set forth in the following 1 claims.

I claim:

1. As a new article of manufacture, a filamentary electronic or like emitter of tungsten of a diameter on the order of .010 of an inch having at least one loop formed in the filament in proximity to the area of emission of the electrons or like particles, for the purpose, of minimizin filament stresses, including those due to the expansion and contraction of said filament in use. 2. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape of tungsten of a diameter on the order of .010 of an inch having a small loop formed in each arm of the filament close to the apex thereof, for the purpose of minimizing filament stresses, including those due to the expansion and con traction of the filament in use.

3. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape of tungsten of a diameter on the order of .010 of an inch having a small loop having an inside diameter on the order of 40 thousandths of an inch formed in each arm of the filament close to the \apex thereof, for the purpose of minimizing filament stresses, including those due to the expansion and contraction of the filament in use.

4. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape of tungsten of a diameter on the order of .010 of an inch having a small loop having an inside diameter on the order of ii) thousandths of an inch at a distance on the order of one eighth of an inch from the apex thereof, for the purpose of minimizing filament stresses, including those due to the expansion and contraction of the filament in use.

5. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape, having lead-in wires, a metallic cup in which said emitter is located and having a small bottom opening wherein is located the apex of the emitter, a porcelain cylinder above and secured to said cup, and steel rods connected to said lead-in wires and passing through said porcelain cylinder and into said cup and therein connected to the two arms respectively of said filamentary emitter of hairpin shape, a tungsten wire secured to each steel rod within said cup and having a Very sharp point very slightly spaced from the said porcelain cylinder to serve as spark gaps to prevent the filamentary emitter from sudden surge discharges.

6. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape, having lead-in wires, a metallic cup in which said emitter is located and having a small bottom opening wherein is located the apex of the emitter, a porcelain cylinder above and secured to said cup, and steel rods connected to said lead-in wires and extending through and sealed to said porcelain cylinder and extending into said cup and there rigidly connected to the two arms respectively of said filamentary emitter of hairpin shape, and tungsten wires upon said steel rods and terminating in very sharp points and constituting spark gaps to prevent the filamentary emitter from sudden surge discharges.

'7. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape, having lead-in wires, a metallic cup in which said emitter is located and having a small bottom opening wherein is located the apex of the emitter, a porcelain member above and secured to said cup and located between said hairpin shape emitter and said lead-in wires and past which current is led from said lead-in wires to said filament, the said porcelain member assisting in minimizing filament stresses by reason of preventing jarring of the filament and eliminating the danger of molten glass on the filament, the portion of the outer surface of said porcelain member that in use is nearest to the said filamentary emitter having secured thereto :an aluminum disk.

8. As a new article of manufacture, a filamentary electronic or like emitter of tungsten wholly of hairpin shape with a sharp apex, the filament being of a diameter on the order of .010 of an inch, having one loop only formed in one arm at least of the filament in close proximity to the area of emission of the electrons or like particles, for the purpose of minimizing filament stresses, including those due to the expansion and contraction of said filament in use, the wall of the loop formation being laterally very slightly twisted so as to be free from side contact with the adjacent portion of the arm of the filament having such loop, whereby such loop is wholly free to expand and to contract in the use of the said filamentary electronic emitter, the entire filamentary emitter being in the plane of the tungsten emitters diameter, such plane having therefore a thickness essentially only that of the filamentary emitter.

9. As a new article of manufacture, a filamentary electronic or like emitter of hairpin shape, comprising a metal cup surrounding said emitter and having in its bottom a central small opening wherein is positioned the apex of said emitter, lead-in wires, a porcelain member located between the hairpin-shaped emitter and said lead-in wires and above said cup, and of the same diameter as said cup and secured thereto, and past which current is led, and steel rods cemented in place in said porcelain member and extending therethrough and rigidly connected to the arms of the said filamentary electronic emitter of hairpin shape, within said cup and to the upper ends of which said lead-in wires are secured.

10. As a new article of manufacture a filamentary electronic or like emitter of hairpin shape, a cup-like metal member surrounding the said emitter, lead-in wires, a porcelain disk-like member of substantially the diameter of said cup and rigidly secured in place above said cup, steel rods connected to said lead-in wires and extending through and sealed in place in said disk-like member and extending into said cup, the two arms of said emitter being welded to said steel rods and an aluminum disk secured in position between the upper edge of said cup and said porcelain member.

11. As a new article of manufacture a filamentary electronic or like emitter of tungsten of hairpin shape and having only one small loop formed in each arm of said filament close to the apex thereof so that said arms of said emitter are otherwise straight except for said two loops, the walls of said loops lying essentially in the plane of the straight portions of said emitter, a metal cuplike member surrounding said emitter and having a small opening in the center of the bottom thereof, and in which the apex of said emitter is positioned, a porcelain member rigidly secured in position at the upper edge of said cup, and of equal diameter therewith, lead-in wires above said cup, steel rods extending from said lead-in wires and sealed in position in said porcelain member and extending through said porcelain member into said cup, the free ends of said hairpin shaped emitter being Welded to opposite sides of the respective steel rods so that the filament apex is centrally located.

12. A filamentary electronic or like emitter in accordance with claim 11, wherein each of said two loops in the arms of the emitter are laterally very slightly twistedso asto bev just free from the adjacent portions of the arms of thefilament, whereby said two loops arewholl y freeto expand and to contract in the use of the filamentary-electronic emitter, notwithstanding that the walls of said loops are essentially in the plane of. the. diameter of the filament of which the emitter is composed.

13. As a new article or manufacture, a fila-v mentary electronic emitter oftungsten wire, of a diameter on the order of .010' of an inch and lying wholly in substantially the same fiat plane of the filaments diameter, said tungsten-wirebeing bent at midlength into hairpin shape having a small, sharp apex, the two arms of the tungsten wire each having a single looponly; each closeto the said sharp apex, each of" said arms extending straight both in front of and in the rear of the loop in said arm, each of said arms near its rear end being bent slightly outwardly, said bends being in opposite directions and providing short terminal portions that are for use of the-filament welded to the opposite sides of two small-dis ameter straight rods respectively, the wall of each of said two loops being very slightly laterally twisted, only sulficiently to be free from side contact with the adjacent straight portion of the arms respectively of the filament having such loop, to permit free expansion and contraction of said loops, said two loops being mirror images of each other and each lying inthe plane of the rest of the wire emitter, the single plane in which the entire said tungsten emitter lies having a thickness exceeding the diameter of the tungsten wire only by the amount at the loops of the said slight lateral twisting of the walls of said two loops respectively, and at theends of the tungsten wire, by the diameter of the two small-diameter straight rods to which the ends of the tungsten wire are for use welded respectively, the entire filamentary emitter being of V-shape with slightly laterally bent ends that are for use welded to the opposite sides respectively of the small-diameter straight rods. 7

14;. As a new article of manufacture, a filamentary electronic emitter of tungsten wire, of a diameter on the order of .010 of an inch and lying wholly in substantially the same fiat plane of the filaments diameter, said tungsten wire being bent at midlength into hairpin shape having a small, sharp apex, at least one of the two arms of the tungsten wire having a single loop only, close to the said sharp apex, each of said arms being otherwise straight and each near its rear end being bent slightly outwardly, said bends being in opposite directions and providing short terminal portions that are welded to the opposite sides of two small-diameter straight rods respectively, the wall of the loop existing in at least one of said arms being very slightly laterally twisted, only sufliciently to be free from side contact with the adjacent straight portion of an arm having such loop, to permit free expansion and contraction of such loop, such loop therefore lying in the plane of the rest of the wire emitter, the single plane in which the entire said tungsten emitter lies having a thickness exceeding the diameter of the wire only by the amount at the one loop at least of the said slight lateral twisting of the wall of the loop, and at the ends of the tungsten wire by the diameter of the two small-diameter straight rods to which the ends of the tungsten wire are welded respectively, the entire filamentary emitter being 10 of V-shape with very slightly laterally bent ends that are welded to the. op osite sides respectively or the small-diameter straight rods.

I5 As a new article of manufacture, a filamentary emitter lying essentially wholly in the fiat plane of the: filaments diameter, said filament being bent at midlength into'hairpin shape having a small, sharp apex, at least one of the two arms of thewire having a. single loop only, close' to the said sharp apex, each of said arms being. otherwise straight and each near its rear end being bent slightly outwardly, said bends being in opposite directions and providing short terminal portions: that are welded to the opposite sides of two small-diameter straight rods respectively, the wall of the loop existing in at least one of said arms being very slightly laterall'y twisted, only sufliciently to be free from side contact-with the adjacent straight portion of an arm having such. loop,-to permit free expansion and contraction of such loop, such loop therefore lying in the plane of the rest of the wire emitter, the single plane in which the entire said emitter lies having a thickness exceeding the diameter of the wire only by the amount at the one loop at least of the said slight lateral twisting of the wall of the loop, and at the ends of the wire by the diameter of the two smallrdiameter rods to which the ends of the wire are welded respectively, the entire filamentary emitter being of V-shape with very slightly laterally bent ends that are welded to the opposite sides respectively of the small-diameter straight rods.

16'. As anew article of manufacture, a filamentary electronic emittter of tungsten wire, of a diameter on the order of .010 of an inch and lying wholly in substantially the same fiat plane of the filaments diameter, said tungsten wire being bent at midlength into hairpin shape having a small, sharp apex, at least one of the two arms of the tungsten wire having a single loop only, close to the said sharp apex, each of said arms being otherwise straight, the wall of the loop existing in at least one of said arms being very slightly laterally twisted; only sufficiently to be free from side contact with the adjacent straight portionof an arm having such loop, to permit free expansion and contraction of such loop, such loop therefore lying in the plane of the rest of the wire emitter, the single plane in which the entire said tungsten emitter lies having a thickness exceeding the diameter of the wire only by the amount at the one loop at least of the said slight lateral twisting of the wire of the loop, the entire filamentary emitter being of V-shape with very slightly laterally bent ends that are welded to the opposite sides respectively of the small-diameter straight rods.

17. As a new article of manufacture, a filamentary emitter lying essentially wholly in the flat plane of the filaments diameter, said filament being bent at midlength into hairpin shape having a small, sharp apex, at least one of the two arms of the wire having a single loop only, close to the said sharp apex, each of said arms being otherwise straight, the wall of the loop existing in at least one of said arms being very slightly laterally twisted, only sufiiciently to be free from side contact with the adjacent straight portion of an arm having such loop, to permit free expansion and contraction of such loop, such loop therefore lying in the plane of the rest of the wire emitter, the single plane in which the entire said emitter lies having a thickness exceeding the diameter of the wire only by 11 the amount at the one loop at least of the said slight lateraly twisting of the wall of the loop, the entire filamentary emitter being of V-shape with very slightly laterally bent ends that are welded to the opposite sides respectively of the small-diameter straight rods;

18. As a new article of manufacture, a filamentary electronic emitter of tungsten wire lying wholly in substantially the same flat plane of the filaments diameter, said tungsten wire being bent at midlength into hairpin shape having a small, sharp apex, at least one of the two arms of the tungsten wire having a single loop only, close to the said sharp apex, each of said arms being otherwise straight and each near its rear end being bent slightly outwardly, said bends being in opposite directions and providing short terminal portions that are welded to the opposite sides of two small-diameter straight rods respectively, the wall of the loop existing in at least one of said arms being very slightly laterally twisted, only sufficiently to be free from side contact with the adjacent straight portion of an arm having such loop, to permit free expansion and contraction of such loop, such loop therefore lying in the plane of the rest of the wire emitter, the single plane in which the entire said tungsten emitter lies having a thickness exceeding the diameter of the wire only by the amount at the one loop at least of the said slight lateral twisting of the wall of the loop, and at the ends of the tungsten wire by the diameter of the two small-diameter straight rods to which the ends of the tungsten wire are welded respectively, the entire filamentary emitter being of V-shape with very slightly laterally bent ends that are welded to the opposite sides respectively of the smalldiameter straight rods, and an enclosure for said the two ends of the filament are welded to the opposite sides of said rods, the otherwise bare lower ends of said small rods extending relatively far into said cup so as to receive the extreme ends of the two arms of said filament.

I 19. An article of manufacture, including a tungsten filament and an enclosure therefor, in accordance with claim 18, wherein between said 1 cylinder and said cup is interposed an aluminum disk of the same diameter as said cup and said cylinder and through which said small-diameter rods extend.

20. An article of manufacture including a tungsten filament and an enclosure therefor, in accordance with claim 18, wherein between said cylinder and said cup is interposed an aluminum disk of the same diameter as said cup and said cylinder and through which said small-diameter rods extend, each of said small rods having therein above the attached upper ends of said filament a surge discharge preventer of tungsten wire having a sharp point serving as a spark gap, and directed toward and extending close to said aluminum disk.

21. An article of manufacture including a tungsten filament and an enclosure therefor, in accordance with claim 18, wherein between said cylinder and said cup is interposed an aluminum disk of the same diameter as said cup and said tungsten filament, having at its lower end a cup receiving said filament and having a small central opening in its bottom wherein is located the apex of said filament, a porcelain-like cylinder of the same diameter as said cup and overlying the same, a serie of screws extending through said cylinder and into the lateral wall of said cup and securing them together, and the said two small rods having lead-in wires secured at their upper ends, said rods extending downward through said cylinder and into said cup, where cylinder and through which said small-diameter rods extend, each of said small rods having therein above the attached upper ends of said filament a surge discharge preventer of tungsten 7 wire having a sharp point serving as a spark gap,

and directed toward and extending close to said aluminum disk, said aluminum disk having pinlike projections extending into said porcelainlike cylinder.

LLOYD R. McINTOSI-I.

References Citedin the file of this patent UNITED STATES PATENTS Number Name Date 1,620,487 Powell Mar. 8, 1927 2,060,610 Cox Nov. 10, 1936 2,304 Boucher et al Dec 8, 1942 2,391,780 Hillier Dec. 25, 1945 2,404,992 Stone July 30, 1946 

